The author combines two theories - one about how multilateral trade liberalization affects regional integration, the other about how it affects political disintegration - to explain why the ratio of free trade areas to customs unions has increased over time. Ethier argues (1998, 1999) that multilateral trade liberalization led to the recent wave of regional integration arrangements. Alesina and others (1997), in discussing the number and size of countries, argue that multilateral trade liberalization leads to political disintegration, with an increase in the number of countries. Combining the two arguments, the author hypothesizes that as multilateral trade liberalization proceeds, and the number of regional integration arrangements increases, the ratio of free trade areas to customs unions also increases. The data, which show that ratio increasing in the 1990s, are consistent with the hypothesis.